1. Field of the Invention
This invention relates to small-sized variable magnification lenses comprised of two lens units suited to lens shutter cameras, video cameras, etc., and, more particularly, to small-sized zoom lenses well corrected for aberrations along with the total length (from the first lens surface to the image plane) shortened by setting forth proper design rules for each lens unit.
2. Description of the Related Art:
Recently, along with reduction of the size of lens shutter cameras, video cameras, etc., there is a growing demand for small-sized zoom lenses of short total length. Even in the field of lens shutter cameras, particularly the compact cameras that are not to interchange the lenses, the use of a zoom lens is looked forward. The zoom lens is nonetheless desired to be as small in size or total length as the monofocal lens used in the past is.
In Japanese Laid-Open Patent Applications Nos. Sho 57-201213, Sho 60-170816, Sho 60-191216 and Sho 62-56917, small-sized zoom lenses are proposed, comprising, from front to rear, a first lens unit of positive refractive power and a second lens unit of negative refractive power, totaling two lens units, the separation between both lens units being varied to vary the magnification. By this, a zoom lens is achieved which employs the arrangement of positive and negative refractive powers in this order from the object side, and whose back focal distance is made relatively short, while still permitting the total length of the lens to be shortened.
Besides these, in Japanese Laid-Open Patent Application No. Sho 62-284319, a zoom lens is disclosed, comprising a first lens unit of positive refractive power and a second lens unit of negative refractive power, the magnification being varied by moving both of the lens units forward while varying the separation between the two lens units.
In the conventional plus-minus 2-unit zoom lenses, there are known a zoom type having a stop in between the first and second lens units and another zoom type having a stop within the first lens unit. In the zoom type having the stop in between the first and second lens units, the barrel construction becomes relatively simple in structure, so that it is easy to hold tolerances for the position of the first lens unit, but it becomes difficult to maintain good correction of aberrations in such a manner that the size is reduced.
Meanwhile, in the zoom type having the stop in the interior of the first lens unit, the structure of the barrel construction tends conversely to increase in complexity, but, because of the stop disposed on the front side, it is easy to afford for an advance in compactness and an increase of the maximum image angle. Further, the aberration correction tends to become relatively easy.